The cessation of the heartbeat is often used as a marker of clinical death. However, some cardiac activity may still occur after a person is declared clinically dead. This has led to questions around whether the heart truly stops at the point of death, or if some residual activity remains for a period of time. In this article, we will explore what happens to heart function after death and examine the evidence around post-mortem cardiac activity.
What defines clinical death?
Clinical death occurs when breathing and blood circulation permanently stop. It is defined by the irreversible loss of function of the heart, lungs, and brain. Clinical death is different from biological death, which is the permanent cessation of all vital bodily functions. Clinical death precedes biological death.
There are two essential criteria that define clinical death:
- Absence of a palpable pulse
- Absence of breath sounds and all respiratory effort
When both these signs are confirmed by a physician, the patient can be declared clinically dead. The diagnosis must be made by a qualified medical professional. The duration of clinical death may vary depending on how it is defined, but it generally lasts from seconds to minutes.
What happens to the heart after clinical death?
Immediately after clinical death is determined, the heart stops beating and circulating blood. However, this does not necessarily mean that all cardiac electrical activity ceases instantly. Research shows that the heart may continue to show some electrical and mechanical activity for a brief period after declaring death.
Here are some key things that may occur:
- Isolated ventricular contractions – Some disorganized electrical activity may cause the ventricles to contract sporadically.
- Slowing electrical activity – The heart’s electrical impulses slow down but do not completely stop.
- Ineffective atrial activity – The upper chambers of the heart (atria) may continue pulsating without pumping blood.
- Reperfusion arrhythmias – Restoring circulation after a period of no blood flow can trigger abnormal heart rhythms.
These residual electrical signals and erratic mechanical movements are due to the last bursts of activity from cardiac muscle cells. They gradually fade as oxygen depletion progresses. Eventually, all cardiac activity ceases as cell death occurs.
How long does electrical activity persist after death?
Studies that have monitored cardiac function after clinical death have found that electrical activity may continue for anywhere between 2-10 minutes.
For example, one study examined the electrical activity in 6 pigs after induced cardiac arrest. Some disorganized electrical activity persisted for up to 4 minutes before being undetectable.
Another study in human patients found that components of electrical impulses were detectable for up to 10 minutes after declaration of death in 85% of cases.
However, the duration varies significantly between cases based on the mechanism and circumstances of death. In most cases, cardiac electrical activity ceases within 2-4 minutes after cessation of circulation.
Does the heart restart after flatlining?
The term “flatlining” refers to a straight, flat heart rhythm tracing on an electrocardiogram (ECG) monitor that indicates no electrical activity. In real life, it is exceptionally rare for the heart to spontaneously resume beating after flatlining.
However, on TV medical dramas, flatlining often portrays a critical medical emergency requiring resuscitating the heart. This depiction creates a misleading perception that the heart may restart after flatlining.
In reality, there are only two highly unusual circumstances in which the heart may spontaneously begin beating again after flatlining:
- Lazarus phenomenon – Very rarely after CPR, the heart can suddenly exhibit organized electrical activity and restart beating. Less than 40 such cases have been reported.
- Autoresuscitation – In extremely rare cases, life-sustaining circulation resumes after a transient period of no blood flow. The mechanism is poorly understood.
Except in these exceptional situations, once a flatline state is reached, the heart will not be able to restore a viable rhythm or pump blood effectively again.
What factors influence post-mortem cardiac activity?
Several factors may impact the presence and duration of residual post-mortem cardiac electrical activity:
- Cause of death – Traumatic causes like hemorrhage or CNS injuries may shorten the duration compared to intrinsic causes like heart failure.
- Electrolyte imbalances – Abnormal potassium, calcium or magnesium levels may allow extended electrical activity.
- Medications – Some drugs like digoxin may prolong the persistence of electrical discharges.
- Body temperature – Cooling slows down cell metabolism and death processes, potentially preserving electrical function briefly.
- Myocardial oxygenation – Reoxygenating the heart experimentally can restore some electrical activity.
These factors help explain why cardiac activity may be sustained for slightly longer in some cases after being declared clinically dead.
What are the implications of prolonged post-mortem electrical activity?
The discovery that cardiac cells may continue to show signs of activity after death has some important implications:
- Our understanding of the precise time when death occurs may need re-evaluation.
- Guidelines for determining death may benefit from more sophisticated criteria.
- Organs used for transplantation may retain better function if recovered shortly after electrical death rather than circulatory death.
- Some consciousness and brain activity could theoretically occur during prolonged electrical activity.
More research is still needed to better characterize post-mortem cardiac activity to inform policies around organ donation and determination of death.
Do pacemakers continue working after death?
Pacemakers are medical devices that deliver electrical impulses to regulate abnormal heart rhythms in patients with arrhythmias. They are powered by batteries implanted under the skin.
Pacemakers will continue sensing heart activity and can still deliver therapy for a brief period after a person dies. The devices are programmed to pace up to a maximum heart rate if they do not detect intrinsic cardiac activity.
One study found that three out of five pacemakers tested continued functioning for up to 90 minutes after patients had died and had no heart beat.
However, pacemakers do not actually restart the heart after death. The residual pacing activities are directed at cardiac tissue that is deteriorating and unable to respond.
Eventually the pacemaker batteries are depleted, or the devices are damaged by acidosis and electrolyte changes that occur with cell death. At this point, they cease functioning entirely.
Can you resuscitate someone after rigor mortis?
Rigor mortis refers to the stiffening of the body after death caused by chemical changes in the muscles. It typically begins 2-6 hours after death and peaks around 12 hours. Rigor mortis starts fading 36 hours after death.
It is not possible to successfully resuscitate someone after the onset of rigor mortis. The changes are irreversible and incompatible with restoring life. Key reasons why resuscitating after rigor mortis will fail include:
- Blood circulation cannot be restarted as blood has coagulated.
- Damaged cell membranes prevent transmission of electrical signals.
- Cross-bridge cycling cannot be resumed to allow muscle contraction.
- Metabolic processes are halted as enzymes leak out of dead cells.
While very rare Lazarus reflex movements may still occur, once rigor mortis commences, there is no physiological possibility of revival or resuscitation.
Conclusion
While the cessation of heartbeat and circulation is considered the endpoint of life, some residual cardiac cell activity may persist for a short time after death in some cases. This activity gradually ceases due to oxygen deprivation and cell death. Under extremely rare circumstances, the heart may spontaneously resume beating after flatlining. However, once rigorous mortis sets in several hours after death, resuscitation is impossible as cell degradation is irreversible. A better understanding of the cardiac electrical patterns in the transition between life and death can improve organ donation policies and resuscitation guidelines.
